Angiogenic endothelial cells are highly specialized for the purpose of forming capillaries de novo. As part of their unique activity, these cells express a cell membrane integrin, alpha-v-beta-3, that mediates endothelial cell-extracellular matrix interactions and is essential for the survival of the angiogenic endothelial cell. In malignancy, tumor growth and metastasis is directly correlated with the angiogenic process, stimulated by tumor- derived factors, andalpha-v-beta-3-expression is a consistent feature of the tumor neovasculature. Because expression of alpha-v-beta-3 is a ubiquitous surrogate marker for the presence of vascularizing metastatic foci, it is an ideal target for cancer therapy and is independent of a tumor's histologic derivation. In this proposal, we will develop a bifunctional fusion protein, mrIL-12vp, that will simultaneously target vascular and immune cell compartments within the tumor microenvironment. The fusion protein contains the small peptide sequence arginine-glycine- aspartic acid (RGD), a ligand for alpha-v-beta-3 that will specifically direct it to angiogenic endothelium within the tumor microenvironment. Solubilized forms of small RGD-containing peptides are antagonistic to alpha-v-beta-3 expression and trigger endothelial cell apoptosis. This vascular homing peptide is coupled to interleukin-12 (IL-12), a cytokine with promising antiangiogenic activity mediated by induction of interferon-gamma and antiangiogenic chemokines. IL-12 is also inhibitory to the production of VEGF and MMP, key factors in the angiogenic process. As a result of targeting by the RGD component, high intratumoral concentrations of IL-12 are anticipated that will also serve to activate tumoricidal responses of immune cells in situ. Experiments will be conducted in tumor-bearing mice designed to demonstrate homing of the fusion protein, localization of IL-12 within the tumor microenvironment, effects on tumor vascularization and growth, contribution of immune cells, and the role of the homing peptide in mediating antiangiogenic properties of this fusion protein. The approach proposed for simultaneously targeting vascular and immune cell compartments within the tumor microenvironment offers an opportunity to develop an innovative strategy to address the significant problems associated with tumor angiogenesis and cytokine therapy.